This invention relates in general to indicating devices and in particular to a new and useful indicating device for respiration filters.
The invention concerns a device for the indication of the exhaustion of gas filters by a color indicator which contains the substance indicating the exhaustion of the filter material in a container that is located inside the filter housing and can be seen through a window from the outside.
The gas filters in respiration equipment, such as masks or at other respirator connections, protect the user against the inhaling of toxic gases. The protection eventually decreases with use. Respirator filters are equipped with indicators that make the remaining time of use visible by optical signs to warn the carrier in time of the imminent exhaustion of the filter material.
A similar device for the indication of the exhaustion of gas filters is known for German DE-PS 694 423. A protective respirator filter with several removable single filters located one behind the other and, which contain also a substance indicating the exhaustion of the filter material, is disclosed therein. The substance is placed behind a window located in the wall of the filter housing. In the practical example the window is screwed into a socket attached to the filter housing. The window may be shaped to form also the receptacle for the indicator. The indicator, however, signals the exhaustion of the filter materials only when the poisonous substance to be kept out has already completely permeated the filter material, which means that the user is not given an early warning, i.e. before the complete exhaustion of the filter material and before the penetration of the poisonous substance.
A respirator filter is known from German DE-PS 703 932 in which the filter material is divided into two layers with a piece of pipe inserted into the filter material from the side where the air escapes. As the harmful poisonous substance penetrates the first layer of the filter material, which extends from the filter entrance uptake to the beginning of the pipe, the user of the equipment will inhale partially unfiltered respiration gas through the piece of pipe, and the user is supposed to notice through his olfactory sense that the filter material is almost completely permeated by the harmful substance to be held back. But such an indication of the exhaustion addresses only the olfactory sense of the user of the equipment, and it is impossible to notice odorless harmful substances with this device in time.
Another colorimetric indicator is already known from German DE-PS 26 23 065 (U.S. Pat. No. 3,966,440). The filter comprises a chamber containing the active filter material with an indicator window adjacent to an opening allowing a view of the chamber interior. The colorimetric indicator material is placed immediately behind the indicator window. It extends partly into the active filter material.
The indicator material, aluminum oxide impregnated with potassium permanganate in this case, changes its red color to brown under the influence of the vinyl compounds to be retained in the filter. This color change occurs with the weakening of the retaining power and takes place in the direction of the filter outlet. A prompt warning is given with the extension of the indicator into the filter material.
Since the indicator material is arranged in the outer periphery of the container holding the filter material, a penetration of the harmful substance can occur even when the indicator material has not yet reached a complete color change, due to differences in the flow rates of the respiration gases within the filter material.